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61.
Waerenborgh JC Tsipis EV Pereira LC Avdeev M Naumovich EN Kharton VV 《Dalton transactions (Cambridge, England : 2003)》2012,41(2):667-678
M?ssbauer spectroscopy and magnetization studies of YBaCo(4-x)Fe(x)O(7+δ) (x = 0-0.8) oxidized at 0.21 and 100 atm O(2), indicate an increasing role of penta-coordinated Co(3+) states when the oxygen content approaches 8-8.5 atoms per formula unit. Strong magnetic correlations are observed in YBaCo(4-x)Fe(x)O(8.5) from 2 K up to 55-70 K, whilst the average magnetic moment of Co(3+) is lower than that for δ ≤ 0.2, in correlation with the lower (57)Fe(3+) isomer shifts determined from M?ssbauer spectra. The hypothesis on dominant five-fold coordination of cobalt cations was validated by molecular dynamics modeling of YBaCo(4)O(8.5). The iron solubility limit in YBaCo(4-x)Fe(x)O(7+δ) corresponds to approximately x ≈ 0.7. The oxygen intercalation processes in YBaCo(4)O(7+δ) at 470-700 K, analyzed by X-ray diffraction, thermogravimetry and controlled-atmosphere dilatometry, lead to unusual volume expansion opposing to the cobalt cation radius variations. This behavior is associated with increasing cobalt coordination numbers and with rising local distortions and disorder in the crystal lattice on oxidation, predicted by the computer simulations. When the oxygen partial pressure increases from 4 × 10(-5) to 1 atm, the linear strain in YBaCo(4)O(7+δ) ceramics at 598 K is as high as 0.33%. 相似文献
62.
E. V. Tsipis V. V. Kharton N. P. Vyshatko A. L. Shaula M. V. Patrakeev J. R. Frade 《Ionics》2003,9(3-4):231-237
Incorporation of alkaline-earth cations into the zircon-type lattice of Ce1−xAxVO4+δ (A=Ca, Sr; x=0−0.2) was found to significantly increase the p-type electronic conductivity and to decrease the Seebeck coefficient,
which becomes negative at x≥0.1. The oxygen ionic conductivity is essentially unaffected by doping. The ion transference numbers
of Ce1−xAxVO4+δ in air, determined by the faradaic efficiency measurements, are in the range from 2×10−4 to 6×10−3 at 973–1223 K, increasing when temperature increases or alkaline-earth cation content decreases. The results on the partial
conductivities and Seebeck coefficient suggest the presence of hyperstoichiometric oxygen, responsible for ionic transport,
in the lattice of doped cerium vanadates. The activation energies for the electron-hole and ionic conduction both decrease
on doping and vary in the ranges 39–45 kJ/mol and 87–112 kJ/mol, respectively.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002. 相似文献
63.
Vladislav A. Kolotygin Ekaterina V. Tsipis Aliaksandr L. Shaula Eugene N. Naumovich Jorge R. Frade Sergey I. Bredikhin Vladislav V. Kharton 《Journal of Solid State Electrochemistry》2011,15(2):313-327
Increasing Sr2+ and Ti4+ concentrations in perovskite-type $ {\left( {{\hbox{L}}{{\hbox{a}}_{0.{75} - x}}{\hbox{S}}{{\hbox{r}}_{0.{25} + x}}} \right)_{0.{95}}}{\hbox{M}}{{\hbox{n}}_{0.{5}}}{\hbox{C}}{{\hbox{r}}_{0.{5} - x}}{\hbox{T}}{{\hbox{i}}_x}{{\hbox{O}}_{{3} - }}_\delta \left( {x = 0 - 0.{5}} \right) $ results in slightly higher thermal and chemical expansion, whereas the total conductivity activation energy tends to decrease. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range (10.8?C14.5)?×?10?6?K?1 at 373?C1,373?K, being almost independent of the oxygen partial pressure. Variations of the conductivity and Seebeck coefficient, studied in the oxygen pressure range 10?18?C0.5?atm, suggest that the electronic transport under oxidizing and moderately reducing conditions is dominated by p-type charge carriers and occurs via a small-polaron mechanism. Contrary to the hole concentration changes, the hole mobility decreases with increasing x. The oxygen permeation fluxes through dense ceramic membranes are quite similar for all compositions due to very low level of oxygen nonstoichiometry and are strongly affected by the grain-boundary diffusion and surface exchange kinetics. The porous electrodes applied onto lanthanum gallate-based solid electrolyte exhibit a considerably better electrochemical performance compared to the apatite-type La10Si5AlO26.5 electrolyte at atmospheric oxygen pressure, while Sr2+ and Ti4+ additions have no essential influence on the polarization resistance. In H2-containing gases where the electronic transport in $ {\left( {{\hbox{L}}{{\hbox{a}}_{0.{75} - x}}{\hbox{S}}{{\hbox{r}}_{0.{25} + x}}} \right)_{0.{95}}}{\hbox{M}}{{\hbox{n}}_{0.{5}}}{\hbox{C}}{{\hbox{r}}_{0.{5} - x}}{\hbox{T}}{{\hbox{i}}_x}{{\hbox{O}}_{{3} - }}_\delta $ perovskites becomes low, co-doping deteriorates the anode performance, which can be however improved by infiltrating Ni and $ {\hbox{Ce}}{{\hbox{O}}_{{\rm{2}} - }}_\delta $ v into the porous oxide electrode matrix. 相似文献
64.
Mössbauer spectroscopy of layered YBaCo3.96Fe0.04O7+δ (δ=0.02 and 0.80), where 1% cobalt is substituted with 57Fe isotope, revealed no evidence of charge ordering at 4-293 K. The predominant state of iron cations was found trivalent, irrespective of their coordination and oxygen stoichiometry variations determined by thermogravimetric analysis. The extremely slow kinetics of isothermal oxidation at 598 K in air, and the changes of Fe3+ fractions in the alternating triangular and Kagomé layers in oxidized YBaCo3.96Fe0.04O7.80, may suggest that oxygen intercalation is accompanied with a substantial structural reconstruction stagnated due to sluggish cation diffusion. Decreasing temperature below 75-80 K leads to gradual freezing of the iron magnetic moments in inverse correlation with the content of extra oxygen. The formation of metal-oxygen octahedra and resultant structural distortions extend the temperature range where the paramagnetic and frozen states co-exist, down to 45-50 K. 相似文献
65.
Solvent shifts induced by the ring current of benzene in several trisdithiocarbamates of arsenic, antimony and bismuth are studied by NMR Spectroscopy. Formation of VAN DER WAALS complexes between trisdithiocarbamates (solute) and benzene (solvent) are proposed. The apparent stoichiometry of the proposed complexes has been found 1:1 and their association constants have been determined from the solvent shifts. The observed solvens shifts and the obtained association constants are correlated to the polarity of C? N bonds in the molecules of dithiocarbamates. 相似文献
66.
Electronic,bonding, and optical properties of 1d [CuCN]n (n = 1–10) chains, 2d [CuCN]n (n = 2–10) nanorings,and 3d [Cun(CN)n]m (n = 4, m = 2, 3; n = 10, m = 2) tubes studied by DFT/TD‐DFT methods
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Athanassios C. Tsipis Alexandros V. Stalikas 《Journal of computational chemistry》2015,36(17):1334-1347
The electronic, bonding, and photophysical properties of one‐dimensional [CuCN]n (n = 1–10) chains, 2‐D [CuCN]n (n = 2–10) nanorings, and 3‐D [Cun(CN)n]m (n = 4, m = 2, 3; n = 10, m = 2) tubes are investigated by means of a multitude of computational methodologies using density functional theory (DFT) and time‐dependent‐density‐functional theory (TD‐DFT) methods. The calculations revealed that the 2‐D [CuCN]n (n = 2–10) nanorings are more stable than the respective 1‐D [CuCN]n (n = 2–10) linear chains. The 2‐D [CuCN]n (n = 2–10) nanorings are predicted to form 3‐D [Cun(CN)n]m (n = 4, m = 2, 3; n = 10, m = 2) tubes supported by weak stacking interactions, which are clearly visualized as broad regions in real space by the 3D plots of the reduced density gradient. The bonding mechanism in the 1‐D [CuCN]n (n = 1–10) chains, 2‐D [CuCN]n (n = 2–10) nanorings, and 3‐D [Cun(CN)n]m (n = 4, m = 2, 3; n = 10, m = 2) tubes are easily recognized by a multitude of electronic structure calculation approaches. Particular emphasis was given on the photophysical properties (absorption and emission spectra) of the [CuCN]n chains, nanorings, and tubes which were simulated by TD‐DFT calculations. The absorption and emission bands in the simulated TD‐DFT absorption and emission spectra have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2015 Wiley Periodicals, Inc. 相似文献
67.
Tsipis E. V. Naumovich E. N. Patrakeev M. V. Yaremchenko A. A. Kovalevsky A. V. Waerenborgh J. C. Kharton V. V. 《Journal of Solid State Electrochemistry》2021,25(12):2777-2791
Journal of Solid State Electrochemistry - Increasing Sr2+ concentration and the creation of A-site deficiency in La1-x-ySrxCoO3-δ (x = 0.3–0.7, y = 0–0.05)... 相似文献
68.
Athanassios C. Tsipis Ioannis G. Depastas Efstathios E. Karagiannis Constantinos A. Tsipis 《Journal of computational chemistry》2010,31(2):431-446
Magnetoresponsive three‐membered rings of d‐ and f‐block elements have been thoroughly investigated with the help of electronic structure calculation methods. The magnetic response of the clusters was evaluated by the Nucleus Independent Chemical Shifts (NICS)zz‐scan curves, which in conjunction with symmetry‐based selection rules for the most significant translationally and rotationally allowed transitions helped rationalize and predict the orbital‐type of aromaticity/antiaromaticity of the clusters. The magnetoresponsive early (Groups 3, 4, and 5) transition metal M3 rings exhibit successive aromatic and antiaromatic zones separated by a nodal plane. The magnetoresponsive late (Groups 11 and 12) transition metal M3 rings exhibit long‐range aromatic zone with the NICSzz(R) values decaying rapidly and monotonically with respect to R. The magnetic response of Group 10 transition metal M3 rings is similar to that of the early transition metal M3 rings, but it is long‐range antiaromatic only for the [c‐Ni3] cluster. The NICSzz‐scan curve of the [(HtLa)3(μ2‐H)6] cluster is indicative of weak pure σ‐aromaticity due to the induced diatropic ring current from the translationally allowed a → e′ and e′ → a transitions. The aromatic–antiaromatic behavior of the [(HtCe)3(μ2‐H)6]+ and [(HtTm)3(μ2‐H)6]2− clusters is similar to that of the early d‐block elements. The magnetic response of [(HtYb)3(μ2‐H)6]3− is similar to that of [c‐Hg3]2−. The [(HtLu)3(μ2‐H)6] cluster can be considered as a doubly (σ + π) aromatic system, with the σ‐aromatic component being much stronger than the π‐aromatic one. Finally, the [(XtRe)3(μ2‐X)6] and [(XtRu)3(μ2‐X)6]+ (X = Cl, Br, I) clusters exhibit significant aromatic character with the greatest contribution to the induced diatropic ring currents coming from π‐type transitions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
69.
Bimetallic Cu(3)Au(3) clusters have been investigated using electronic structure calculation techniques (DFT) to understand their electronic, magnetic, and optical properties as well as the geometrical structures. The most stable homotop is the planar cyclo-[Cu(3)(micro-Au)(3)] form consisting of a triangular positively charged Cu(3) structural core with negatively charged Au atoms occupying exposed positions. This structure is characterized by the maximum number of heterobonds and peripheral positions of Au atoms. Possible growth formats of the cyclo-[Cu(3)(micro-Au)(3)] homotops have been explored following both the edge-capping and the stepwise metal atom substitution mechanism. The bonding pattern along with the density of states (DOS) plots of the cyclo-[Cu(3)(micro-Au)(3)] homotop are thoroughly analyzed and compared with those of the pure cyclo-[Cu(3)(micro-Cu)(3)] and cyclo-[Au(3)(micro-Au)(3)] clusters. Particular attention was paid on the stability of these bimetallic clusters in relation with the ring-shaped electron density distribution (aromaticity). It was found that all 3-membered metal rings exhibit significant aromatic character, which was verified by a number of established criteria of aromaticity, such as structural, energetic, magnetic (NICS profiles), and out-of-plane ring deformability criteria. The NICS (1) values correlate well with the out-of-plane ring deformation energy. Finally, a comprehensive analysis of the optical spectra of the CuAu, Cu(2), and Au(2) diatomics and the cyclo-[Cu(3)(micro-Au)(3)], cyclo-[Cu(3)(micro-Cu)(3)], and cyclo-[Au(3)(micro-Au)(3)] clusters placed the electronic assignments of the optical transitions on a firm footing. 相似文献
70.
J. R. Frade V. V. Kharton A. A. Yaremchenko E. V. Tsipis 《Journal of Solid State Electrochemistry》2006,10(2):96-103
In order to evaluate the applicability of concentration cells for the ion transference number measurements with external load,
the cell response was simulated with variable transport properties of the cell material, external load resistance, geometrical
factors such as ion-conducting membrane thickness, and electrode kinetics. This technique is expected to be pertinent when
ηF/RT<0.2, except possibly for conditions when the electrode kinetics is dependent on a relatively small limiting current density.
In each particular case, the method validity can be verified by testing if the overpotential sum grows faster than current
on decreasing the external load resistance. A pyrochlore-type material Gd1.9Ca0.1Ti2O7-δ with dominant oxygen ionic conductivity is used as a study case to demonstrate the criteria proposed to assess the applicability
of emf measurements under short-circuit conditions. 相似文献